A method for evaluation of analgesic activity of drugs using heat-inflamed foot of rat

Abstract

In order to evaluate analgesic activity of drugs administered for pain related to inflammation, a new assay method was devised with special reference to the behavior of heat-injured rat. Thermal injury was given to the hind foot of a rat by dipping it in hot water of 57°C for 5 sec under ether anesthesia and the inflammatory pain was produced by means of applying additional heat stimulation (40°C, 5 sec) to the same foot 2 to 4 hr after the first thermal procedure. The assay was based on a graded response, the duration of foot-lifting behavior being counted over a 30 sec period. Results obtained are as follows : The pain reaction is specifically inhibited by analgesics. Aside from the anti-inflammatory activity, the analgesic activity of non-steroidal anti-inflammatory drugs appeared to be more selective than when the yeast-inflamed foot method was used. The pain reaction time could be determined under less restricted environmental conditions than with the threshold method. Relative potencies of activity among anti-inflammatory drugs in this test were : indomethacin>flufenamic acid>mefenamic acid> bimetopyrol>ibuprofen>phenylbutazone>aminopyrine> aspirin.